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Recent evidence has demonstrated that there are fluctuations in both the anatomy and physiology of the hippocampus across the estrous cycle of the female rat. In the present study we examined the behavioral implications of these changes by testing females on either a hippocampal or nonhippocampal version of the Morris water maze during the various phases of the estrous cycle. Males were also tested on these tasks. Although there was little variance on the nonhippocampal cue task, females in proestrus performed significantly better than those in estrus. Optimal female performance on the spatial version of the task occurred during the phase of estrus, whereas the least efficient performance occurred during proestrus. These results do not support the traditional view that hippocampal long-term potentiation is positively correlated with spatial learning.

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There is recent evidence of continuing development throughout adolescence in two neural areas involved in emotion and cognition, the basolateral amygdala (BLN) and the medial prefrontal cortex (mPFC). Previous research from our laboratory has demonstrated a cellular loss in both of these brain regions in rats between postnatal day (P) 35 and 90. This study investigates dendritic changes in pyramidal neurons of the BLN and Layer 5 of the mPFC at P20 (juvenile), 35 (puberty), and 90 (adulthood) in hooded rats of both sexes. Dendritic branching and dendritic spines were quantified in Golgi-Cox impregnated tissue. Between P20 and 35, dendritic length and complexity, as well as the density of dendritic spines, increased in both structures. Between P35 and 90, dendritic spines in the mPFC neurons significantly decreased in both sexes, while a loss of basilar dendrites was only detected in females. In the BLN, there was an increase in the number of branches between P35 and 90 without an increase in the total length of the dendritic tree. BLN spine density also remained stable during this period. These results show that the dendritic tree grows prior to puberty while dendritic remodeling and pruning occurs after puberty in both of these neural areas. This late development may lead to susceptibilities to psychopathologies and addictions that often develop at this time.